Coated articles and/or devices with optical out-coupling layer stacks (OCLS), and/or methods of making the same

ABSTRACT

Certain example embodiments relate to organic light emitting diode (OLED) inclusive devices, and/or methods of making the same. A substrate supports a transparent conductive coating (TCC) based layer, and first and second organic layers disposed thereon. A reflective conductive layer is supported by the organic layers. An out-coupling layer stack (OCLS) interposed between the organic layers and a viewer of the device includes a hybrid organic-inorganic polymer matrix having scatterers dispersed throughout in a manner such that each scatterer is located in the far field of its nearest neighbor. The scatterers are dispersed to have a high Zeta potential, and promote Mie-like scattering of light passing through the OCLS. Mie-like scattering caused by the OCLS may help to frustrate the wave-guiding modes in the glass, e.g., by breaking down the in-phase coherence.

Certain example embodiments relate to coated articles and/or deviceswith optical out-coupling layer stacks (OCLS), and/or methods of makingthe same. More particularly, certain example embodiments relate toout-coupling layer stacks including Mie-like “soft” scatters that helpreduce waveguide modes in OLED and/or other device, devices includingthe same, and/or methods of the above.

BACKGROUND AND SUMMARY OF CERTAIN EXAMPLE EMBODIMENTS

An organic light emitting diode (OLED) is a light-emitting diode (LED)in which the emissive electroluminescent layer is a film of organiccompounds which emit light in response to an electric current. Thislayer of organic semiconductor material is situated between twoelectrodes in some cases. Generally, for example, at least one of theseelectrodes is transparent. OLEDs (based on polymers and/or evaporablesmall molecules) sometimes are used in television screens; computermonitors; small or portable system screens such as those found on mobilephones and PDAs; and/or the like. OLEDs may also sometimes be used inlight sources for space illumination and in large-area light-emittingelements. OLED devices are described, for example, U.S. Pat. Nos.7,663,311; 7,663,312; 7,662,663; 7,659,661; 7,629,741; and 7,601,436,the entire contents of each of which are hereby incorporated herein byreference.

A typical OLED comprises two organic layers—namely, electron and holetransport layers—that are embedded between two electrodes. The topelectrode typically is a metallic mirror with high reflectivity. Theanode is typically a transparent conductive layer supported by a glasssubstrate. The top electrode generally is the cathode, and the bottomelectrode generally is the anode. Indium tin oxide (ITO) often is usedfor the anode.

FIG. 1 is an example cross-sectional view of an OLED. The glasssubstrate 102 supports a transparent anode layer 104. The holetransmitting layer 106 may be a carbon nanotube (CNT) based layer insome cases, provided that it is doped with the proper dopants.Conventional electron transporting and emitting and cathode layers 108and 110 also may be provided.

When a voltage is applied to the electrodes, the charges start moving inthe device under the influence of the electric field. Electrons leavethe cathode, and holes move from the anode in opposite direction. Therecombination of these charges leads to the creation of photons withfrequencies given by the energy gap (E=hv) between the LUMO and HOMOlevels of the emitting molecules, meaning that the electrical powerapplied to the electrodes is transformed into light. Different materialsand/or dopants may be used to generate different colors, with the colorsbeing combinable to achieve yet additional colors.

The technology has desirable attributes such as large viewing angle,fast response time, high contrast, and a Lambertian profile.

Although significant progress has been made on the electronic quality ofthe emissive and charge carrier layers, a significant portion of thelight emitted is trapped by both the ITO coating on the glass and theunderlying glass substrate, e.g., as wave-guiding modes promoted byinterference effects. Because of this inefficiency, some of thesedevices are driven at higher current densities than what normally wouldbe required. This unfortunately has a negative influence on theirlifetimes. Even under these non-nominal driving conditions, the luminousefficiency of OLEDs can be significantly below that of fluorescentlamps.

It would be desirable to improve the light output of an OLED device,e.g., through a light out-coupling strategy. Doing so could improve thelifetime and/or overall luminous efficiency of the device. Severaltechniques have been proposed to improve the light efficiency, but thesemethods unfortunately do not meet the practical requirements ofmanufacturability.

As alluded to above, there have been several attempts to improvetechniques for light extraction efficiency. For example, an attempt hasbeen made to increase the extraction from the substrate into the air byway of adding micro-refractive or diffractive structures (e.g., arraysof micro-lenses or pyramids, scattering layers, etc.) to the substratesurface. Depending on the reflectance of the OLED stack, the extractionfrom the substrate into the air can be increased considerably, typicallyup to 30%. Unfortunately, however, these structures tend to be quitefragile.

Another attempt relates to monochromatic light emitting devices. In suchdevices, the angular distribution of the light emitted into thesubstrate depends on the layer thicknesses of the OLED stack (e.g., byvirtue of the micro-cavity effect). By proper design, the amount oflight in the escape cone of the substrate can be increased and externalefficiencies of up to 40% can be reached at the design wavelength.

Still another approach involves harnessing the “organic modes” thatrepresent about 50% of the generated photons by the introduction ofordered or random scattering structures into the OLED stack. There is adrawback, however, in terms of a possible negative influence on theelectrical performance, inasmuch as the anode would be rough, andlocalized current hot spots that are detrimental to device performancecan develop.

A persistent challenge involves attempts at matching the refractiveindex of the glass substrate and the organic layers so that the organicmodes are turned into substrate modes. The amount of light extractedinto the substrate can indeed be increased by a factor 2-3, at leasttheoretically.

Provided that the OLED has a highly reflective cathode and is thickenough, 80% of the photons generated inside the OLED can be extractedinto a high index substrate. However, the remaining issue is still thento out-couple this light into air without reverting back to one of theabove-described strategies.

FIG. 2 shows different major light modes in connection with a schematicview of an OLED device. As can be seen, the major modes include a lightin air mode (A), a light in glass mode (B), and a light trapped in theorganic layers and/or the ITO. It will be appreciated that there may bemore “B-modes” where the glass is thicker and/or more absorptive. It isnoted that there also is another component related to Plasmon losses inthe cathode, although this is not depicted in the FIG. 2 schematic view.

In view of the foregoing, it will be appreciated that there is a need inthe art for techniques for improving the light emitting efficiencies ofOLED devices.

One aspect of certain example embodiments relates to a lightout-coupling layer stack (OCLS) on a substrate (e.g., on a glasssubstrate), with a view towards reducing wave-guiding modes.

Another aspect of certain example embodiments relates to scalabletechniques for achieving higher luminous efficiency in OLEDs.

Certain example embodiments relate to a method of making an electronicdevice is provided. An optical out-coupling layer stack (OCLS) isdisposed, directly or indirectly, on a substrate. A layer comprising atransparent conductive coating (TCC) (e.g., a transparent conductiveoxide or TCO) is disposed, directly or indirectly, on the OCLS. One ormore light emitting layers is/are disposed, directly or indirectly, onthe layer comprising the TCC. A layer comprising conductive material isdisposed, directly or indirectly, on the one or more light emittinglayers. The OCLS comprises an isotropic layer matrix including anorgano-metallic chelate hybrid material and a matrix core includingdispersed scatterers. The OCLS has an index of refraction of at leastabout 1.8. The dispersed scatterers have a Mie-like scatteringefficiency of greater than 1, leading to an index matching out-couplingefficiency for the OCLS of greater than 1.

Certain example embodiments relate to a method of making an organiclight emitting diode (OLED) inclusive device is provided. A layercomprising a transparent conductive coating (TCC) is disposed, directlyor indirectly, on a glass substrate. First and second organic layers aredisposed, directly or indirectly, on the layer comprising the TCC. Alayer comprising a conductive material is disposed, directly orindirectly, on the one or more light emitting layers, with the layercomprising conductive material being reflective. An optical out-couplinglayer stack (OCLS) is disposed, directly or indirectly, on thesubstrate, with the OCLS including an isotropic layer matrix includingan organo-metallic chelate hybrid matrix with scatterers dispersedtherein. A relative refractive index m of the OCLS, a size r of thescatterers, and a concentration of the scatterers (1/s³) are selected soas to increase the total integrated light out-coupled from the device toa level where total out-coupling efficiency for the device is greaterthan it would, if no OCLS were provided.

Certain example embodiments relate to an organic light emitting diode(OLED) inclusive device is provided. A glass substrate is provided. Alayer comprising a transparent conductive coating (TCC) is supported bythe substrate. First and second organic layers are supported by thelayer comprising the TCC. A reflective conductive layer is supported bythe first and second organic layers. An out-coupling layer stack (OCLS)is interposed between the organic layers and a viewer of the device. TheOCLS includes a hybrid organic-inorganic polymer matrix havingscatterers dispersed throughout in a manner such that each scatterer islocated in the far field of its nearest neighbor. The scatterers aresized, shaped, and positioned relative to one another so as to (a) havea high Zeta potential, and (b) promote Mie-like scattering of lightpassing through the OCLS.

These and other embodiments, features, aspect, and advantages may becombined in any suitable combination or sub-combination to produce yetfurther embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages may be better and morecompletely understood by reference to the following detailed descriptionof exemplary illustrative embodiments in conjunction with the drawings,of which:

FIG. 1 is an example cross-sectional view of an OLED;

FIG. 2 shows different major light modes in connection with a schematicview of an OLED device;

FIG. 3 shows the efficiency of the index matching layer matrix ofcertain example embodiments as a function of wavelength and angle ofincidence;

FIGS. 4 a and 4 b schematically show mono-dispersed scatterers withdifferent inter-distance spacings, and with different Zeta potentials;

FIG. 5 a is a graph plotting the scattering efficiency of one scattererin connection with certain example embodiments;

FIG. 5 b shows half angular distributions for Γ(θ) at the top half ofthe graph, and Γ(φ) at the bottom half of the graph, at differentscattering angles, in accordance with certain example embodiments;

FIG. 6 is a schematic view of a slot meniscus coater, dispensing amatrix with scatterers, in accordance with certain example embodiments;

FIG. 7 is a graphical formulation of the light trapping problem to besolved;

FIG. 8 is a schematic cross-sectional view of an OLED device accordingto certain example embodiments;

FIG. 9 is an enlarged view of the OCLS system shown in the FIG. 8example;

FIG. 10 is a graph showing theoretical luminous efficiencies, integratedover a half sphere, as a function of wavelength for different scattererdensities; and

FIG. 11 is a graph plotting the actual emission spectrum from twoexample PLED devices.

DETAILED DESCRIPTION OF CERTAIN EXAMPLE EMBODIMENTS

A significant amount of emitted light from an organic light emittingdiode (OLED) may be trapped as a result of total internal reflection(TIR) within several layers and interfaces (e.g., the lightemitting-anode, anode-glass, and glass-air interfaces). It has beenobserved that only about 50% of the light emitted makes it into theglass substrate, with the trapped being absorbed within theanode/organic layers/cathode layer stack. Certain example embodimentsincrease the light extraction efficiency by combining both an indexmatching layer, as well as a total internal reflection (TIR) frustratingmedium on one or both sides of the glass in a manner that helps improveforward scattering of light. For example, a model of the current OLEDstructure is developed based on the Mie-Lorenz theory and, based on thismode, it is possible to simulate and optimize forward Mie scattering bysolving for the S matrix. Provided the cathode is perfect reflector,almost 100% of light trapped by the TIR can be extracted if the radiusof the scatters, scatterer index profile, refractive index ratio betweenthe matrix and the scatterer, and concentration of the scatterers arecarefully selected. The light extraction is defined by the equation,Γo/Γ_(i)=η_(imL)×η_(s). Certain example embodiments make use of thisapproach and involve an OCLS layer stack system. Data is provided tosupport the beneficial effect in the case of spherical scatterers in ahigh index matrix. While certain example embodiments may be used inconnection with solid state light sources, the example approachesdescribed herein may additionally or alternatively be used in otherapplications where light extraction for a distributed light source overa certain solid angle is necessary or desirable.

As indicated above, certain example embodiments help improve the lightemitting efficiencies of OLED devices, e.g., through an opticalout-coupling layer stack (OCLS) system. An OCLS may help to provide anindex matching layer between the glass and ITO/organic stack (and/orpolymer LED stack), e.g., to help increase the light otherwise coupledinto the glass. Mie-like scattering caused by the OCLS may help tofrustrate the wave-guiding modes in the glass, e.g., by breaking downthe in-phase coherence. In a related manner, Mie-like forward scatteringmay be increased, even with reduced spectral dispersion.

For example, Γ_(i)(Ω, k) can be defined as the photon flux incident tothe glass surface, and Γ_(o)(Ω, k) can be defined as the output flux inair, where the symbols Ω and k are solid angle and wave vector,respectively. The ratio is now boosted by a factor η_(iml)×η_(s)(Ω, k),where η is the index matching efficiency of the OCLS matrix/adjacentplanarizer and where η_(s) is the scattering efficiency. The total fluxoutput can the be calculated by computing the double integral ∫∫Γ_(i)(Ω,k)η_(iml)×η_(s)(Ω, k)dΩdk over the entire phase space. However, based onthis model, one can see that the necessary condition is that the productη_(iml)×η_(s)>1. Certain example embodiments described below demonstratehow this regime can be implemented.

The OCLS may be a multilayer system in certain example embodiments, withits functionality being based at least in part on how its variouscomponents are optimized so as to achieve the desired performance. Incertain example embodiments, the OCLS may include a thick isotropiclayer matrix, with a matrix layer core that includes dispersed sphericalscatterers, and an optional planarization layer. Each of thesecomponents is discussed in greater detail, below.

As indicated above, the OCLS may include a thick isotropic layer matrix,e.g., located between the glass and anode. This layer may include anorgano-metallic chelate hybrid with a high refractive index, preferablygreater than 1.7, more preferably of 1.8-1.9, and potentially evenhigher in some cases. The absorption coefficient may be near zero insome cases. The chemistry of the matrix layer is described in, forexample, U.S. Publication No. 2012/0088319, the entire contents of whichare hereby incorporated herein by reference.

As the '319 publication describes, certain example embodiments mayinvolve hybrid coating systems based on polymeric titanium dioxideand/or polymeric zirconia based systems. The organic-inorganic hybridpolymer solution is prepared by first reacting the titanium alkoxidewith a chelating agent to convert the highly reactive tetra-coordinatetitanium species to a less reactive hexa-coordinate species. Otherdesired polymer components may then be added to the stabilized titaniumcontaining solution and thoroughly mixed. As a result of thestabilization, the hybrid polymer solution may be stable at roomtemperature up to 6 months with negligible change in color andviscosity. The hybrid polymer solution may be spin-coated or verticalslot coated onto substrates to a desired thickness.

A titanium dioxide rich film was generated by thermally decomposing thehybrid coatings at an elevated temperature of less than about 250degrees C. The resulting dried films may be made as thin as 0.2 um andup to about 4 um or more. Such films may have good transparency and haverefractive indices as high or higher than about 1.90 in the entirevisible region when the cure temperature was 300 degrees C. or higher. Acrack-free film over 300 nm in thickness was obtained with a singlecoating application. Multiple-coating is applicable to obtain a thickerfilm, and no apparent interface was seen from SEM cross-section imagesbetween two consecutive coatings. The hybrid high refractive index filmsare mechanically robust, stable upon exposure to both heat and UVradiation, and may be applicable for a wide variety of opticalapplications. The material is compatible with semiconducting material.

In certain example embodiments, the organic-inorganic hybrid polymer maybe introduced into a laminable medium such as ethylene-vinyl acetate(EVA), silicones, aramids, etc. This would then allow the use of vacuumbonding or de-airing, sometimes without the use of autoclave.

The organic polymers chosen contained multiple hydroxy functionalities.They were so chosen to allow primary or secondary chemical bondingbetween the polymer and the titanium dioxide phase to promote phasecompatibility and a high degree of dispersion. The chelated poly(dibutyltitanate) polymer and the organic polymer are compatible in all orsubstantially all proportions, both in solution and in the cured film,as evidenced by their high transparency and the refractive indexdispersion curves. Typically, an index as high as or higher than 1.9 isobtained at 550 nm for a thickness of 0.4 um. When deposited on anyinorganic light emitting diode, even a film as thin as 0.4 micronsdramatically improves the light out-coupling from the high refractiveindex material significantly typically in the incremental range of 70%.

An inorganic-based precursor is provided. In certain exampleembodiments, the inorganic-based precursor may be a titanium-basedprecursor such as, for example, titanium alkoxide, a titanium-basedphosphate complex, etc. The inorganic-based precursor may be depositeddirectly or indirectly on the device and/or substrate to be coated. Forinstance, in certain example embodiments, a titanium alkoxide basedprecursor may be deposited via atomic layer deposition (ALD), atitanium-based phosphate layer may be printed, etc. Of course, it willbe appreciated that other high-index inorganic materials may be used inplace of or in addition to the titanium in certain example embodiments.

A chelate may be formed, and an organic component may be added, togetherwith optional additives. The chelate in certain example instances may besalicylic acid. The organic component in certain example embodiments maybe a resin, silicone, polyimide, polyamide, and/or the like. Optionaladditives also may be introduced. For instance, other inorganicmaterials (e.g., in place of or in addition to the titanium-basedprecursor) may be introduced to tune the index of refraction. Indeed,the index of refraction may be adjusted upwardly or downwardly byselective inclusion of zirconia, silica and/or silicates, etc. Lightscattering elements and/or heat dissipating elements also may beintroduced. One example material that functions both as a lighterscattering agent and a heat dissipater is boron nitride. Plasticizersalso may be included in certain example embodiments.

The chelated titanium-based precursor and the organic component(s) maybe cross-linked to create an organic-inorganic hybrid solution. In oneexample, titanium alkoxide may be reacted with a chelating agent toconvert the tetra-coordinate Ti species into a less reactivehexa-coordinate species, e.g., to create chelated poly(dibutyltitanate). Of course, other titanates may be created and/or used indifferent embodiments of this invention. The hybrid polymer may resultin certain example instances by mixing together the chelatedpoly(dibutyl titanate) with a hydroxy inclusive organic resin. Incertain example embodiments, the organic and inorganic components may beprovided in equal percentages by weight. In certain example embodiments,the organic and inorganic components may be provided in a ratio of 60/40by weight. Of course, other ratios and/or percentages are possible indifferent embodiments of this invention.

The hybrid solution may be quite liquidous in certain exampleembodiments. In such a case, the hybrid solution may be wet applied,vertical slot meniscus coated, or otherwise provided to a desiredthickness. Example coating techniques are described in, for example,U.S. Pat. No. 6,383,571, the entire contents of which are herebyincorporated herein by reference. In certain example embodiments,however, it may be desirable to provide a more viscous hybrid laminate(e.g., inorganic and/or other materials included in an organic bindersuch as EVA, silicones, aramids, etc.) that can be extruded, forexample. A more viscous hybrid laminate may be advantageous in terms ofa “cleaner” or “less messy” application.

The coated hybrid polymer or laminate is dried and/or cured. The dryingand/or curing may help to remove solvents and water, leaving moreinorganic material than organic material in certain example embodiments.The drying may take place at a first elevated temperature of less thanabout 250 degrees C., whereas the curing may take place at a secondelevated temperature of greater than or equal to about 300 degrees C.Certain example embodiments may include one or both of drying and curingat these and/or any other suitable temperature.

Thus, in summarizing these example basic formulation, cross-linking, andcuring steps, it will be appreciated that a chelated Ti-based precursoris brought into contact with a resin binder; the resin binder and thechelated Ti-based precursor are cross-linked; the solvent is evaporatedthrough a heating process, and the cured film is adhered to a substrate(e.g., a film, hard surface, glass, etc.). In so doing, either (a) theorganic-inorganic hybrid solution is wet applied on the substrate overthe at least one LED, or (b) the organic-inorganic hybrid solution isintroduced into a carrier medium and then the carrier medium is extrudedonto the substrate over the at least one LED. The organic-inorganichybrid solution is cured once disposed on the substrate, e.g., informing the coating.

The rheological property of the matrix preferably is such that it can bedispensed either by zone casting or a slot meniscus coating over largeareas of glass, and rapidly cured, e.g., by heat and/or UV exposure.When cured, it may help to effectively index match to the anode (e.g.,ITO inclusive) and light emitting (e.g., organic) layers. In some cases,this portion of the OCLS may be 10-100 um in thickness. The smoothnessof this layer preferably is on the order of the smoothness of glass andhas an RMS roughness of less than or equal to 1.0 nm and more preferablyof less than or equal to about 0.5 nm.

One of the routes for the matrix implementation is the use of glassypolymeric monomer to which titanium, hafnium, and/or zirconiumoxo-clusters are added. When polymerization of the monomer is done inthe presence of 10-30% by weight of Zr₄O₂(OMc)₁₂, for example, a clearand high index film is produced with high flexural strength andextremely good adhesion to the glass substrate. The use of anappropriate surfactant and coupling agent may assist in slot dispensinguniformity. The organic surface of Ti₁₆O₁₆(OEt)₃₂ cluster can beselectively modified by alcoholysis. This gives rise to new functionalclusters, Ti₁₆O₁₆(OEt)₃₂-x(OR)x, where R can be a methacrylate orstyrene and x is the number of modified alkoxy ranging anywhere from 4to 16 depending, for example, on the pH.

The resulting matrix thus combines advantages of polymers (e.g.,processability, flexural strength, etc.) and those of inorganic buildingblocks (such as, for example, high refractive index in the case of thetransition alkaloids and chemical inertness, thermal and environmentalstability, etc.). The index matching layer (imL) alone has goodout-coupling efficiencies for incidence angles near zero and is alsoangle dependent.

FIG. 3 shows the efficiency of the imL matrix of certain exampleembodiments as a function of wavelength and angle of incidence. Arefractive index of 1.9 at 500 nm and a dispersion typical of themetallo-organic polymer was used in generating the FIG. 3 data, e.g., inaccordance with the '319 publication.

The matrix layer core includes generally spherical scatterers thatpreferably are dispensed in such a manner that they are not clumpedtogether. The Zeta potential of the scatterer colloid used preferably ishigh for good stability of the system, and sometimes is even greaterthan 70 mV. As is known, the Zeta potential refers to electro-kineticpotential in colloidal systems. Zeta potential is the potentialdifference between the dispersion medium and the stationary layer offluid attached to the dispersed particle. Those skilled in the artgenerally consider a value of 25 mV as the value that separateslow-charged surfaces from highly-charged surfaces. It is noted that theZeta potential value sometimes is related to the stability of thecolloidal dispersion, e.g., such that high values indicate greaterstability, etc. These values also help ensures that the scattererfilling density is in a range of values such that the spheres aremono-dispersed with an inter-particle distance d of about 3sphere-diameters (or 6r). If this condition is met, then theirseparation is sufficiently large so that contribution of secondary wavesto the field exciting each particle is much smaller that the externalfield.

The total scattered field therefore can be approximated by the sum ofscattered fields generated by an individual independent scatterer. Thisregime is called a single scattering event. In this regime, eachscatterer preferably is located in the far field of its nearestneighbor, and preferably there is no systematic phase relationship. Oneexception is the case of exact forward scattering, which is generallyalways coherent. In the other extreme, when the density of particles islarge, then each particle scatters light that has already been scatteredby other particles. This condition gives rise to diffuse scattering,which can have a large backscatter response. The condition of diffusescattering can be promoted by setting a threshold limit to scattererdensity. The scatterers thus may be produced in a manner so that theyhave a surface static charge and, when placed in the pre-cured matrixlayer, helps keeps the particles apart. The scatterers can be made of anoptically soft but low k material (e.g., refractive index less thanmedium and thus, for example, somewhere between 1.3-1.7, for instance),such that the ratio of ns/nl=m<1. However one can use values such thatm≧1 in other example embodiments.

FIGS. 4 a and 4 b schematically show mono-dispersed scatterers withdifferent inter-distance spacings, and with different Zeta potentials.In FIG. 4 a, the inter-distance s is greater than 3d, which helps toensure a single scatter. The Zeta potential in FIG. 4 a is high, e.g.,at a value greater than 75 mV. By contrast, FIG. 4 b shows agglomeratedor clustered scatters in a high-index isotropic matrix. The Zetapotential in FIG. 4 b is low, e.g., at about of about 10 mV.

FIG. 5 a is a graph plotting the scattering efficiency of one scattererin connection with certain example embodiments. The graph is a functionof x=2πrm/λ, where the symbols π, r, and λ keep their usual meanings,and where m is the relative refractive index ratio (ns/nm). In theregime of single scatter event, the total scatter function is asummation of all scatters in a given volume. FIG. 5 b shows half angulardistributions for Γ(θ) at the top half of the graph, and Γ(φ) at thebottom half of the graph, at different scattering angles, in accordancewith certain example embodiments. Both functions are substantiallysymmetrical about the horizontal axis. Thus, it can be seen from FIG. 5b that there are two half curves that are (i) the polar (top half) and(ii) Azimuthal (bottom half) of the scattering distribution function. Itwill be appreciated that plot (i) could be drawn in its entirety bybasically reflecting about the x axis of the curve, and that the sameapplies to plot (ii). Because each half plot is substantially symmetricabout the x axis, a measure of how the whole scattering function worksis conveyed.

FIG. 6 is a schematic view of a slot meniscus coater, dispensing amatrix with scatterers, in accordance with certain example embodiments.In the FIG. 6 embodiment, the coater is stationary as the substrate 600moves relative to it, although this need not always be the case indifferent example embodiments (e.g., the coater may move while thesubstrate 600 is stationary). The material to be coated is inserted intothe coater at an inlet 602. Excess material is at least temporarily heldin a cavity 604, as the remainder proceeds down the slot 606. The widthh of the slot 606 is helps in the formation of the meniscus 608proximate to the slot exit 610.

Of course, it will be appreciated that higher or lower separations maybe provided in certain example embodiments. It also will be appreciatedthat the scatterers need not necessarily be perfectly spherical andother shapes (e.g., eye-shaped spheres, oblong spheres, etc.) may beused (and potentially “mixed and matched”) in different exampleembodiments. Cylinders also may be used and may prove beneficial in somecases, e.g., as a result of their anisotropy.

An optional planarization layer may be over-coated onto the cured matrixand scattering layers. The planarization layer may comprise a zinc-basedchelate (e.g., a ZnO-inclusive polymer layer), and may help to annealout roughness remaining from the scattering layer. This layer can bedispensed by a slot meniscus coater and cured, by heat and/or UV. Aftercuring, the ZnO-inclusive polymer layer also may help act as a seed forthe anode disposed thereon. For instance, this planarization layer mayserve as a seed for an ITO inclusive film that is deposited by, forexample, MSVD or other suitable process. The planarization layertherefore may be compatible with the ITO deposition and processingtechniques.

It therefore will be appreciated that a transparent conductive oxide(TCO), such as ITO or the like, may be disposed directly or indirectlyon the planarization layer. This TCO may help to ensure that the finalOLED stack is function in an electro-optically desirable manner.However, the TCO layer need not necessarily be considered a part of theOCLS in all example embodiments.

One natural modeling approach to aid in understanding light trapping inOLED devices is based on ray tracing techniques. Such techniques alsomay be used to model many properties of the scattering matrix.Unfortunately, however, ray tracing is somewhat disadvantageous in thatit tends to underestimate backscattering. Thus, certain exampleembodiments advantageously make use of the Mie Scattering Model. Thescattering coefficients an, bn, cn and dn, and are calculated, and thescattering matrix is computed. The amplitude of the scattered field canthen be computed as a function of the incident field:

$\left( \frac{E_{||s}}{E_{\bot s}} \right) = {\frac{e^{{ik}{({r - z})}}}{- {ikr}}\begin{pmatrix}S_{2} & S_{3} \\S_{4} & S_{1}\end{pmatrix}\left( \frac{E_{||i}}{E_{\bot i}} \right)}$

The elements of the amplitude scattering matrix in general depend on thescattering angle and the azimuthal angle. Stokes parameters (whichgenerally refer to the set of values that describe the polarizationstate of electromagnetic radiation) are incorporated into the amplitudescattering matrix, and the procedure as per van de Hulst (e.g., in“Light Scattering by Small Particles,” Dover Books on Physics, 1981) maybe followed. In order to test the validity of the assumption, the onsetof multiple scattering may be computed for simple spherical scatterers,the radiative transfer method described per Chandrasekhar (e.g., in“Radiative Transfer,” Dover Books on Physics, 2011) may be followed.

FIG. 7 is a graphical formulation of the light trapping problem to besolved. A two-dimensional cross-sectional array of dielectric rods ofdiameter b=2R in a periodic square lattice, with a period a=S, is shownin the in the FIG. 7 formulation.

Referring once again to FIG. 5 a, it can be seen that the first maximumin the scattering efficiency where x is equal to about 4. With anx-value of 4 and for a value of m equal to about 0.45, this correspondsto a value of d of from about 0.8-1.6 microns. Now, using the conditionthat s is about 3*d, one achieves a number density ranging from 0.5 to 1particle per cubic micron, depending on the packing density. Theseparameters also explain why the thickness of the scattering layer to bein the order of at least 10 microns.

Effective medium approximation (EMA) refers to physical models thatdescribe the macroscopic properties of a medium based on the propertiesand relative fractions of its components. The following equations mayhelp determine the effective medium approximation (EMA) for the matrixin the different modes:

For the transverse magnetic mode where there is no magnetic field in thez direction (TMz mode), with p polarization:

$ɛ_{eff} = {ɛ_{0} + {{\frac{\pi^{2}}{3}\left\lbrack {f\left( {1 - f} \right)\left( {ɛ_{2} - ɛ_{1}} \right)} \right\rbrack}{{}_{}^{}{}_{}^{}}} + {O\left( \alpha^{4} \right)}}$

For the transverse electric mode where there is no magnetic field in thez direction (TEz mode), with s polarization:

$ɛ_{eff} = {\frac{1}{a_{0}} + {{\frac{\pi^{2}}{3}\left\lbrack {{f\left( {1 - f} \right)}\frac{\left( {ɛ_{2} - ɛ_{1}} \right)}{ɛ_{2}ɛ_{1}}} \right\rbrack}^{2}\frac{ɛ_{0}}{a_{0}^{3}}\alpha^{2}} + {O\left( \alpha^{4} \right)}}$

The symbols (e.g., π and ∈_(eff)) take their usual meanings. Inaddition, in the above equations:

${a_{0} = {\frac{f}{ɛ_{2}} - \frac{\left( {1 - f} \right)}{ɛ_{1}}}},{ɛ_{0} = {{ɛ_{2}f} - {ɛ_{1}\left( {1 - f} \right)}}},{{{and}\mspace{14mu}\alpha} = {\frac{2R}{\lambda_{0}}.}}$

It is noted that the refractive index n of the OCLS may be equal toabout the square root of epsilon. The index may be graded in certainexample embodiments, e.g., as a function of the thickness (or z-axis) ofthe OCLS. The grading may be from nearly n=2 (e.g., if the anode is ofor includes ITO) down to about 1.5 towards the glass. It also is notedthat it is possible in certain example embodiments to use a metal gridinstead of ITO for the anode. For instance, the grid may be coated witha field matrix hole injection layer followed by the EL layer and, inthis particular case, the index of the OCLS may be graded from about1.88 to the value of glass, e.g., as a function of z.

In certain example embodiments, the scatterers may get smaller near thesurface, e.g., in terms of the diameters or major distances of thevarious distributions. For instance, the size may be graded from a 2micron average diameter or major distance to 0.5 microns and even to ananometric level at the surface.

FIG. 8 is a schematic cross-sectional view of an OLED device accordingto certain example embodiments, and FIG. 9 is an enlarged view of theOCLS system shown in FIG. 8. As shown in FIGS. 8-9, the OCLS systemcomprises the matrix portion 802 a and the planarizer portion 802 b. TheOCLS system is interposed between the substrate 102 and the anode 104(e.g., of or including ITO). The Mie-like scatterers included in thematrix portion 802 a help reduce the total amount of internalreflections, which otherwise would in large part constitute “lostlight.” Example thicknesses of the various layers and the roughness ofthe planarizer portion 802 b are set forth above. The FIG. 8 cathode 110may be reflective, e.g., to help reduce TIR. In some cases, reflectanceof the cathode 110 is greater than 50%, more preferably greater than75%, and still more preferably greater than 80%. In some cases, thereflectance may be 85-90%, or even higher.

In certain example embodiments, the scattering layer may alternativelyor additionally be placed on surface 1 of the glass. Doing so may insome cases increase the probability of out-coupling, while at the sametime helping to attenuate reflection from the OLED. Scratch resistance,environmental stability, and/or other ruggedness aspects of the OCLSsystem may be enhanced to help it survive this potentially more harshenvironment.

FIG. 10 is a graph showing theoretical luminous efficiencies, integratedover a half sphere, as a function of wavelength for different scattererdensities. As can be seen from the FIG. 10 graph, higher scatteringdensities translate into higher theoretical luminous intensities at allwavelengths.

The FIG. 11 graph generally confirms the more theoretical FIG. 10 graph.That is, FIG. 11 is a graph plotting the actual emission spectrum fromtwo example PLED devices. The lower line in FIG. 11 represents a PLEDdevice that lacks an OCLS system, whereas the upper line corresponds toa PLED device having an OCLS system with a 35 micron thick scattererlayer that has been planarized. In the latter example, the anodeincluded a layer comprising ITO supported by a seed layer comprisingzinc oxide, and the layer comprising ITO was ion beam etched, e.g., soas to improve its smoothness. The scatterers used were optically softsilicate spheres in a Ti based chelate.

As will be appreciated from the above, in certain example scenarios, theindex matching out-coupling efficiency (>1) is boosted by a Mie-likescattering efficiency greater than one. The matrix containing thescatterers is itself a high index inorganic chelate. The scatterers areprepared, e.g., so that they comprise one or more materials. Forinstance, scatterers may have a concentric composition that increasesscattering in some cases. The relative refractive index m, size r, andconcentration of the scatterers (1/s³) are chosen so that they helpimprove total integrated light out-coupled from the devices.

In certain example embodiments, the OCLS system may have one or more ofthe following and/or other advantageous characteristics:

-   -   Ability to induce forward scattering;    -   Ability to redirect light waveguide modes;    -   Ability to promote Mie-like scattering, thereby reducing (and        sometimes even eliminating) spectral dispersion;    -   Hygroscopic scatterer material, with possible getters;    -   Non-clumping and non-absorbing scatterer and matrix;    -   Planarizer index-matched to underlying layers (e.g., ITO AND        light emitting organic layer compositions); and/or    -   Compatibility with vacuum deposition and heat treatments        (including those typically used, e.g., in ITO deposition).

Certain example embodiments may be used in connection with soda limesilicate glass, and/or so-called low-iron glass. For instance, thesubstrate 102 in FIG. 8, for example, may be a low-iron glass substrate.Low-iron glass is described in, for example, U.S. Pat. Nos. 7,893,350;7,700,870; 7,557,053; 6,299,703; and 5,030,594, and U.S. PublicationNos. 2006/0169316; 2006/0249199; 2007/0215205; 2009/0223252;2010/0122728; 2010/0255980; and 2011/0275506. The entire contents ofeach of these documents is hereby incorporated herein by reference.

Although certain example embodiments have been described in connectionwith OLEDs and/or PLEDs, it will be appreciated that the techniquesdescribed herein may be used in connection with other types of lightemitting diodes (LEDs) including, for example, inorganic light emittingdiodes, and/or other lighting systems, etc.

In certain example embodiments, a method of making an electronic deviceis provided. An optical out-coupling layer stack (OCLS) is disposed,directly or indirectly, on a substrate. A layer comprising a transparentconductive coating (TCC) is disposed, directly or indirectly, on theOCLS. One or more light emitting layers is/are disposed, directly orindirectly, on the layer comprising the TCC. A layer comprisingconductive material is disposed, directly or indirectly, on the one ormore light emitting layers. The OCLS comprises an isotropic layer matrixincluding an organo-metallic chelate hybrid material and a matrix coreincluding dispersed scatterers. The OCLS has an index of refraction ofat least about 1.8. The dispersed scatterers have a Mie-like scatteringefficiency of greater than 1, leading to an index matching out-couplingefficiency for the OCLS of greater than 1.

In addition to the features of the previous paragraph, in certainexample embodiments, the matrix may include a polymeric monomer to whichoxo-clusters are added.

In addition to the features of the previous paragraph, in certainexample embodiments, the oxo-clusters may include Ti, Hf, and/or Zroxo-clusters.

In addition to the features of either of the two previous paragraphs, incertain example embodiments, polymerization of the monomer may beperformed in the presence of 10-30% by weight of Zr₄O₂(OMc)₁₂.

In addition to the features of any of the four previous paragraphs, incertain example embodiments, the matrix may at least initially have anorganic surface including Ti₁₆O₁₆(OEt)₃₂ that is modified and/or ismodifiable by via alcoholysis.

In addition to the features of the previous paragraph, in certainexample embodiments, the alcoholysis may create new functional clustersincluding Ti₁₆O₁₆(OEt)_(32-x)(OR)_(x).

In addition to the features of the previous paragraph, in certainexample embodiments, R may be a methacrylate or styrene, and x may bethe number of modified alkoxys, x preferably being between 4 and 16,inclusive.

In addition to the features of any of the seven previous paragraphs, incertain example embodiments, the scatterers may be generally sphericaland/or generally cylindrical.

In addition to the features of any of the eight previous paragraphs, incertain example embodiments, a filling density of the scatterers may bein a range of values such that the scatterers are mono-dispersed with aninter-particle distance d of about 3 diameters or major distances.

In addition to the features of the previous paragraph, in certainexample embodiments, each scatterer may be located in the far field ofits nearest neighbor and there may be no systematic phase relationship,except for coherent exact forward scattering.

In addition to the features of either of the two previous paragraphs, incertain example embodiments, the refractive index for the OCLS may be1.8-1.9, and the absorption coefficient for the OCLS may be at or near0.

In addition to the features of any of the 11 previous paragraphs, incertain example embodiments, the electronic device may be an organiclight emitting diode (OLED) inclusive device, wherein the one or morelight emitting layers may comprise first and second organic layers, andwherein the layer comprising conductive material may be reflective.

In addition to the features of any of the 12 previous paragraphs, incertain example embodiments, a planarization layer may be disposedbetween the matrix and the layer comprising the TCC.

In addition to the features of the previous paragraph, in certainexample embodiments, the RMS roughness of the planarization layer may beless than 1.0 nm.

In addition to the features of the previous paragraph, in certainexample embodiments, the planarization layer may comprise a zinc-basedchelate.

In certain example embodiments, a method of making an organic lightemitting diode (OLED) inclusive device is provided. A layer comprising atransparent conductive coating (TCC) is disposed, directly orindirectly, on a glass substrate. First and second organic layers aredisposed, directly or indirectly, on the layer comprising the TCC. Alayer comprising a conductive material is disposed, directly orindirectly, on the one or more light emitting layers, the layercomprising conductive material being reflective. An optical out-couplinglayer stack (OCLS) is disposed, directly or indirectly, on thesubstrate, the OCLS including an isotropic layer matrix including anorgano-metallic chelate hybrid matrix with scatterers dispersed therein.A relative refractive index m of the OCLS, a size r of the scatterers,and a concentration of the scatterers (1/s³) are selected so as toincrease the total integrated light out-coupled from the device to alevel where total out-coupling efficiency for the device is greater thanit would, if no OCLS were provided.

In addition to the features of the previous paragraph, in certainexample embodiments, the matrix may include a polymeric monomer to whichoxo-clusters are added.

In addition to the features of the previous paragraph, in certainexample embodiments, the scatterers may be generally spherical and havea Zeta potential greater than 70 mV.

In addition to the features of any of the three previous paragraphs, incertain example embodiments, a filling density of the scatterers may bein a range of values such that the scatterers are mono-dispersed with aninter-particle distance d of about 3 diameters or major distances.

In addition to the features of any of the four previous paragraphs, incertain example embodiments, the OCLS may be located on a surface of thesubstrate opposite the first and second organic layers.

In certain example embodiments, an organic light emitting diode (OLED)inclusive device is provided. A glass substrate is provided. A layercomprising a transparent conductive coating (TCC) is supported by thesubstrate. First and second organic layers are supported by the layercomprising the TCC. A reflective conductive layer is supported by thefirst and second organic layers. An out-coupling layer stack (OCLS) isinterposed between the organic layers and a viewer of the device. TheOCLS includes a hybrid organic-inorganic polymer matrix havingscatterers dispersed throughout in a manner such that each scatterer islocated in the far field of its nearest neighbor, the scatterers beingsized, shaped, and positioned relative to one another so as to (a) havea high Zeta potential, and (b) promote Mie-like scattering of lightpassing through the OCLS.

In addition to the features of the previous paragraph, in certainexample embodiments, there may be no or substantially no systematicphase relationship in connection with the dispersed scatterers, exceptfor coherent exact forward scattering.

In addition to the features of either of the two previous paragraphs, incertain example embodiments, the matrix may include a polymeric monomerto which Ti, Hf, and/or Zr oxo-clusters are added.

In addition to the features of the previous paragraph, in certainexample embodiments, the refractive index for the OCLS may be 1.8-1.9,and the absorption coefficient for the OCLS may be at or near 0.

In addition to the features of any of the four previous paragraphs, incertain example embodiments, the layer comprising the TCC may compriseindium tin oxide and may be set up as an anode, and wherein thereflective conductive layer may be set up as a cathode.

As used herein, the terms “on,” “supported by,” and the like should notbe interpreted to mean that two elements are directly adjacent to oneanother unless explicitly stated. In other words, a first layer may besaid to be “on” or “supported by” a second layer, even if there are oneor more layers there between.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of making an electronic device, themethod comprising: disposing an optical out-coupling layer stack (OCLS),directly or indirectly, on a substrate; disposing a layer comprising atransparent conductive coating (TCC), directly or indirectly, on theOCLS; disposing one or more light emitting layers, directly orindirectly, on the layer comprising the TCC; and disposing a layercomprising conductive material, directly or indirectly, on the one ormore light emitting layers, wherein the OCLS comprises an isotropiclayer matrix including an organo-metallic chelate hybrid material and amatrix core including dispersed scatterers, wherein the OCLS has anindex of refraction of at least about 1.8, and wherein the dispersedscatterers have a Mie-like scattering efficiency of greater than 1,leading to an index matching out-coupling efficiency for the OCLS ofgreater than
 1. 2. The method of claim 1, wherein the matrix includes apolymeric monomer to which oxo-clusters are added.
 3. The method ofclaim 2, wherein the oxo-clusters include Ti, Hf, and/or Zroxo-clusters.
 4. The method of claim 2, wherein polymerization of themonomer is performed in the presence of 10-30% by weight ofZr₄O₂(OMc)₁₂.
 5. The method of claim 1, wherein the matrix at leastinitially has an organic surface including Ti₁₆O₁₆(OEt)₃₂ that ismodified and/or is modifiable by via alcoholysis.
 6. The method of claim5, wherein the alcoholysis creates new functional clusters includingTi₁₆O₁₆(OEt)_(32-x)(OR)_(x).
 7. The method of claim 6, wherein R is amethacrylate or styrene, and x is the number of modified alkoxys, xbeing between 4 and 16, inclusive.
 8. The method of claim 1, wherein thescatterers are generally spherical and/or generally cylindrical.
 9. Themethod of claim 1, wherein a filling density of the scatterers is in arange of values such that the scatterers are mono-dispersed with aninter-particle distance d of about 3 diameters or major distances. 10.The method of claim 9, wherein each scatterer is located in the farfield of its nearest neighbor and there is no systematic phaserelationship, except for coherent exact forward scattering.
 11. Themethod of claim 9, wherein the refractive index for the OCLS is 1.8-1.9,and the absorption coefficient for the OCLS is at or near
 0. 12. Themethod of claim 1, wherein the electronic device is an organic lightemitting diode (OLED) inclusive device, wherein the one or more lightemitting layers comprises first and second organic layers, and whereinthe layer comprising conductive material is reflective.
 13. The methodof claim 1, further comprising disposing a planarization layer betweenthe matrix and the layer comprising the TCC.
 14. The method of claim 13,wherein the RMS roughness of the planarization layer is less than 1.0nm.
 15. The method of claim 14, wherein the planarization layercomprises a zinc-based chelate.
 16. A method of making an organic lightemitting diode (OLED) inclusive device, the method comprising: disposinga layer comprising a transparent conductive coating (TCC), directly orindirectly, on a glass substrate; disposing first and second organiclayers, directly or indirectly, on the layer comprising the TCC;disposing a layer comprising a conductive material, directly orindirectly, on the one or more light emitting layers, the layercomprising conductive material being reflective; and disposing anoptical out-coupling layer stack (OCLS), directly or indirectly, on thesubstrate, the OCLS including an isotropic layer matrix including anorgano-metallic chelate hybrid matrix with scatterers dispersed therein,wherein a relative refractive index m of the OCLS, a size r of thescatterers, and a concentration of the scatterers (1/s³) are selected soas to increase the total integrated light out-coupled from the device toa level where total out-coupling efficiency for the device is greaterthan it would, if no OCLS were provided.
 17. The method of claim 16,wherein the matrix includes a polymeric monomer to which oxo-clustersare added.
 18. The method of claim 17, wherein the scatterers aregenerally spherical and have a Zeta potential greater than 70 mV. 19.The method of claim 16, wherein a filling density of the scatterers isin a range of values such that the scatterers are mono-dispersed with aninter-particle distance d of about 3 diameters or major distances. 20.The method of claim 16, wherein the OCLS is located on a surface of thesubstrate opposite the first and second organic layers.